General configuration of electronic component mounting machines is shown in FIG. 3. A printed wiring board 3 is supplied on a transfer rail 2 from the side of a mounting machine 1, and positioned at a specified mounting area. A suction head 8 picks up by suction a component set in a parts feeder 4 disposed at the front of the mounting machine 1, transfers the component over the printed wiring board 3, and mounts it at a specified position on the printed wiring board 3.
The suction head 8 of the prior art employs a suction nozzle unit 9 at its tip as shown in FIG. 4. The suction nozzle unit 9 has a suction face 12 at the tip of its nozzle body 11 for holding an electronic component 10. A concave portion 13 for suction is formed at the center of the suction face 12, and is led to an inlet hole 14 perforated through the vertical direction along the nozzle body 11. A fitting groove 18 is disposed at the outer edge of the tip of the nozzle body 11. An O-ring 17 is fitted and fixed to the fitting groove 18, slightly protruding from the suction face 12. The suction nozzle unit 9 is connected to a vacuum generator (not illustrated) by means such as a hollow shaft.
For holding the electronic component 10 by suction, as shown in FIG. 4, the suction head 8 lowers and the suction face 12 of the suction nozzle unit 9 is pressed against the surface of the electronic component 10. The O-ring 17 deforms as illustrated by its own elasticity, and tightly contacts the surface of the electronic component 10 to form an airtight seal around the suction face 12. Then, when the vacuum pressure in the concave portion 13 for suction increases as the vacuum generator is operated, the surface of the electronic component 10 sticks to the suction face 12 and the O-ring 17. Here, the electronic component 10 is securely held by preventing air leakage with the O-ring 17 and keeping a specified vacuum pressure in the concave portion 13 for suction. After the electronic component 10 is transferred to above the specified position on the printed wiring board 3, the vacuum generator stops vacuuming operation, allowing the surface of the electronic component 10 to be released from the suction face 12 and the O-ring 17.
An advantage of the suction head 8 employing the above conventional suction nozzle unit 9, compared to existing suction nozzle units which use a diamond, is its reliable holding power by means of improvement of the vacuum rate for the electronic component 10 with the use of the O-ring 17. On the other hand, however, the O-ring 17 may not smoothly separate from the electronic component 10 when the vacuum is switched off at mounting the electronic component 10 on the printed wiring board 3, due to its own viscosity, because the O-ring 17 is made of a material such as rubber. In some cases, the electronic component 10 sticks to the O-ring 17 as the suction head 8 rises, and the component bounces or slightly moves on the printed wiring board 3. Therefore, the prior art has a disadvantage in mounting the electronic component 10 accurately on the printed wiring board 3, making it difficult to realize high density mounting of electronic components 10.